Laser systems that output high-quality beams can be used in a number of applications. For example, low-noise, high-power amplifiers could be used in telecommunication systems to support the transport of information over very long distances. Some laser systems use fiber amplifiers to amplify light, meaning the light is amplified within optical fibers that are transporting the light. A fiber amplifier generally includes a core and a cladding around the core, where light travels through the core and is amplified by active lasing ions within the core.
There are a number of fiber amplifiers that have been developed over the years. One goal of fiber amplifier designs has been to increase a core's cross-sectional area without compromising an output beam's quality. A larger core area increases the energy-storage capacity of the fiber due to the larger volume of doped material in the core. This can be particularly beneficial for pulsed laser systems or other high-energy laser systems since it reduces optical intensity in the core and increases thresholds for deteriorating nonlinear effects.
Some fiber amplifiers have included large circular cores, but scaling up the size of a circular core typically decreases an output beam's quality. As a result, fiber amplifiers with other core shapes have been developed, such as rectangular cores. However, fiber amplifiers with rectangular cores are highly multi-mode in their larger dimension, which can lead to difficulties in maintaining high output beam qualities.